1. Field of Invention
This invention relates to a confocal system, and more particularly to such system which does not require scanning in the direction of the optical axis.
2. Description of the Prior Art
Conventional confocal systems provide confocal images in the following manner. A disk having a plurality of apertures is rotated. A sample is scanned by focusing thereon light beam which is passed through the apertures. A three dimensional shape of the sample, based on cross sectional images, is obtained by scanning the sample a plurality of times in the optical axis direction.
FIG. 1 shows a conventional confocal system comprising a light source 1, a confocal scanner 2, an optical microscope 3, a stage 4 on which a sample is placed, a detector 5, such as a camera, and a controller 6, such as a computer. Output light from the laser 1 is made incident on the confocal scanner 2 through an optical fiber or the like. Scanner 2 rotates a disk having a plurality of apertures therein and passes the laser light beam through the apertures. Optical microscope 3 focuses the light beam outputted from confocal scanner 2 onto a sample (not shown) placed on stage 4. Stage 4 drives the sample in the direction of the optical axis of the incident light. Furthermore, detector 5 is provided in confocal scanner 2 and an output signal from detector 5 is supplied to controller 6.
Operation of the system of FIG. 1 is as follows. Light beam is focused on the sample by optical microscope 3 after passing through the apertures of the disk of scanner 2. The sample reflects the light and the reflected (or otherwise called "return") light is again passed through the apertures of the scanner disk and is made incident on detector 5. The images obtained by detector 5 are confocal images. Since the disk is rotated, the spot of light focused on the sample scans the sample surface. Detector 5 then obtains cross sectional images of the sample on planes perpendicular to the direction of the optical axis.
A three dimensional image of the sample can be determined by storing the multiple cross sectional images obtained of the sample by scanning the sample in the direction of the optical axis by controlling stage 4, and then by reconstructing the cross sectional images. These procedures are performed in the controller 6.
That is, a three dimensional shape can be derived by storing a plurality of cross sectional images in planes perpendicular to the direction of the optical axis while scanning the sample in the direction of the optical axis by controlling stage 4 and by reconstructing the cross sectional images using controller 6.
However, in the confocal system of FIG. 1, a long measuring time is required to obtain one three dimensional image because scanning is done by utilizing stage 4 and in the optical axis direction to obtain the plurality of cross sectional images. Thus, if the conventional system is used, for example in factory automation, semiconductor production lines, etc, the length of measuring time presents a difficult problem. Also, another problem is that stage 4 must be provided separately and the accuracy of measurement then depends solely on the driving accuracy of the stage.